1. Field of the Invention
The present invention relates to a hybrid optical waveguide circuit chip used for optical transmissions, and in particular a method for predicting the optical characteristics of an optical waveguide circuit and a hybrid optical waveguide circuit chip whose structure is improved so that such prediction is enabled.
2. Description of the Related Art
There is available a hybrid optical waveguide circuit chip as one of the methods for increasing the productivity of optical modules used in the field of optical transmissions and for lowering production cost thereof. The hybrid optical waveguide circuit chip is such that optical elements are mounted on an optical waveguide circuit having an optical element incorporating portion, and it has been noted that productivity thereof is excellent, and integration of various optical waveguides and optical elements is enabled.
A description is given of a prior art hybrid optical waveguide circuit chip with reference to FIG. 6. The prior art hybrid optical waveguide circuit chip 5 has the structure shown in FIG. 6. That is, it is composed so that a lower cladding layer 20 is formed on a silicon (Si) substrate 10 and an optical waveguide layer 80 is formed thereon. The first optical waveguide circuit 1 having two cores 1A and 1B is formed on the optical waveguide layer 80. Light receiving and emitting elements 3a and 3b are optical elements incorporated in an optical element incorporating portion 10a, etc., which is provided at an appointed position of a hybrid optical waveguide circuit chip 5. The ends 1a and 1b at one side of the cores 1A and 1B of the first optical waveguide circuit 1 are terminated at the chip end face A of one side of the hybrid optical waveguide circuit chip 5, and the ends at the other side of the cores 1A and 1B of the corresponding first optical waveguide circuit 1 are terminated at respective end faces C and D of the optical waveguide layer 80 facing the boundary portion at the surrounding area 3 of the optical element incorporating portion.
It is necessary that the optical characteristics of the first optical waveguide circuit 1 formed in the hybrid optical waveguide circuit chip 5 are measured before shipment of the chip 5. However, if the optical characteristics are measured after optical elements are incorporated in the optical element incorporating portion, such a disadvantage arises in that the optical elements once incorporated will become useless if the measured values slip outside the standards or the limits. Therefore, if an attempt to measure the optical characteristics is made before incorporating the optical elements in the optical element incorporating portion to avoid the above disadvantage, the optical elements could not be measured by connecting optical fibers to both end faces of a chip because the other ends 1c and 1d of the cores 1A and 1B of the first optical waveguide circuit 1 are not terminated at the other chip end face B of the hybrid optical waveguide chip 5. That is, the end faces 1c and 1d of the cores 1A and 1B are terminated at the end face of the optical waveguide layer 80 having a level gap with respect to the surface of the silicon substrate 10, wherein because the height of the optical axis of the end faces 1c and 1d from the surface of the silicon substrate 10 is less than the radius of the optical fibers, it becomes difficult for the end faces 1c and 1d and the optical fibers to be connected with the optical axes aligned with each other.
Based on the above description, it is highly necessary that, before incorporating optical elements in the chip 5, the optical characteristics of the first optical waveguide circuit 1 of the hybrid optical waveguide circuit chip are easily measured and predicted at high accuracy. However, no method applicable to real applications has been developed yet.
The present invention was developed to solve the abovementioned shortcomings and problems, and it is therefore an object of the invention to provide a hybrid optical waveguide circuit chip having the following construction. That is, the invention provides a hybrid optical waveguide circuit chip comprising an optical element incorporating portion in which optical elements are incorporated, and a first optical waveguide circuit optically connected to said optical elements, wherein a second optical waveguide circuit is disposed adjacent to said first optical waveguide circuit, one end face of said second optical waveguide circuit is terminated at one chip end face of the hybrid optical waveguide circuit chip, and at least one of the optical waveguide end faces at the other end face of said second optical waveguide circuit is terminated at the other chip end face of the hybrid optical waveguide circuit chip.
A hybrid optical waveguide circuit chip according to another aspect of the invention is featured in that one end face of the first optical waveguide circuit at said hybrid optical waveguide circuit chip is terminated at one chip end face of the hybrid optical waveguide circuit chip, and the other end face of said first optical waveguide circuit is terminated at the respective end faces of optical waveguide layers at the boundary portion at the surrounding area of the optical element incorporating portion.
A hybrid optical waveguide circuit chip according to further another aspect of the invention is featured in that portions which determine the appointed optical characteristics of both the first optical waveguide circuit and the second optical waveguide circuit in said hybrid optical waveguide circuit chip are formed so as to have the same shape.
A hybrid optical waveguide circuit chip according to still another aspect of the invention is featured in that the first and second optical waveguide circuits in the hybrid optical waveguide circuit chip are optical waveguide circuits of a two-by-two directional coupler.
A hybrid optical waveguide circuit chip according to further another aspect of the invention is featured in that that the first and second optical waveguide circuits in the hybrid optical waveguide circuit chip are Mach-Zehnder type optical waveguide circuits.
Also, the present invention provides a method for predicting characteristics of the hybrid optical waveguide circuit chip, which comprises the steps of measuring optical characteristics of said second optical waveguide circuit by utilizing a second optical waveguide circuit having a termination end at both end faces of the hybrid optical waveguide circuit chip and predicting the optical characteristics of the measured second optical waveguide circuit as substantial optical characteristics of the first optical waveguide circuit.
The invention provides another method for predicting characteristics of the hybrid optical waveguide circuit chip, which comprises the steps of sampling one of a plurality of hybrid optical waveguide circuit chips formed from the same wafer; measuring the optical characteristics of the second optical waveguide circuit of the sampled hybrid optical waveguide circuit chip by utilizing the second optical waveguide circuit having a termination end at both end faces of the sampled hybrid optical waveguide circuit chip; and predicting the optical characteristics of the measured second optical waveguide circuit as substantial optical characteristics of the first optical waveguide circuits of all the hybrid optical waveguide circuit chips formed from the same wafer.
According to the invention, the second optical waveguide circuit is formed in the same hybrid optical waveguide circuit chip and both ends of at least one of optical waveguides of the corresponding second optical waveguide circuit are terminated at both chip end faces of the hybrid optical waveguide circuit chip, whereby such an excellent effect can be brought about, by which the optical characteristics of the first optical waveguide circuit, which are very difficult to be directly measured, can be predicted (or evaluated) from the results of measurement of optical characteristics of the second optical waveguide circuit for which the measurement is easy.